Objects/textures not showing when using command line render (Blender 2.5x)
The problem was that I created the scenes using blender 2.66, but invoked Blender 2.58 on the command line; there are backwards compatibility issues involved here although I forgot exactly what it was (something to do with ngons I believe). Regardless the end result is that precious few object types created in 2.66 will load in 2.58 so the real surprise here was that anything was displayed at all.

Thanks for everybody who kindly tried helping with this. Took me a while to track the issue as I usually need to keep several versions of blender installed so I guess this 'issue' wouldn't affect many people.